1. Field of the Invention
The invention described herein is related to data communication. More specifically, the invention is related to embedding pilot information into data at a transmitter for obtaining channel state information at a receiver.
2. Description of the Prior Art
Multiple-input multiple-output (MIMO) communication systems beneficially provide high capacity data communication with greater reliability than their single channel counterparts. Space-time (ST) coding has engendered transmit diversity so as to significantly improve the bit error rate (BER) of data transmission without an increase in transmission power. However, a major challenge in realizing such systems lies in providing the coherent detector with channel state information, which is a measure of the effects of the channel on the propagation of the signal. Typically, channel state information is estimated from a known signal transmitted through the channel for such purpose, where the known signal is commonly referred to as a training signal or pilot signal. Training signal techniques are widely applicable and are desirable when low computational complexity is inherent to their implementations.
Common pilot-aided channel estimation techniques for single-input single-output (SISO) and MIMO systems include the pilot symbol assisted modulation (PSAM) technique and the pilot-embedding technique. In PSAM, a pilot signal is time-multiplexed into the transmit data stream, which is then extracted at the receiver and used to ascertain the channel state information. Interpolation of multiple channel estimates is applied over a certain time period to improve accuracy. However, the signal from which channel information is derived is sparsely transmitted, which results in poor state tracking of the channel with respect to time. Unfortunately for these PSAM systems, increasing the time-density of the pilot signal consumes bandwidth otherwise used for real data and thus penalizes the system's efficiency.
Pilot-embedding, also referred to as the pilot-superimposed technique, adds a sequence of pilot signals directly to the data stream. Channel estimation and data detection are accomplished at the receiver through a soft-decoding procedure, such as the Viterbi algorithm. This technique achieves better bandwidth efficiency over PSAM since no time slots are sacrificed for pilot signal use. The pilot-embedding technique does, however, involve higher computational costs in the decoder and a longer delay in the channel estimation process.
The need exists in the field of data communication for channel state information acquisition, which is computationally affordable and able to track channels states in fast-fading channels.